How to subscribe to other class' events in C#?

Question

A simple scenario: a custom class that raises an event. I wish to consume this event inside a form and react to it.

How do I do that?

Note that the form and custom class are separate classes.

Answer 1

public class EventThrower
{
    public delegate void EventHandler(object sender, EventArgs args) ;
    public event EventHandler ThrowEvent = delegate{};

    public void SomethingHappened() => ThrowEvent(this, new EventArgs());
}

public class EventSubscriber
{
    private EventThrower _Thrower;

    public EventSubscriber()
    {
        _Thrower = new EventThrower();
        // using lambda expression..could use method like other answers on here

        _Thrower.ThrowEvent += (sender, args) => { DoSomething(); };
    }

    private void DoSomething()
    {
       // Handle event.....
    }
}

Answer 2

Inside your form:

private void SubscribeToEvent(OtherClass theInstance) => theInstance.SomeEvent += this.MyEventHandler;

private void MyEventHandler(object sender, EventArgs args)
{
    // Do something on the event
}

You just subscribe to the event on the other class the same way you would to an event in your form. The three important things to remember:

1. You need to make sure your method (event handler) has the appropriate declaration to match up with the delegate type of the event on the other class.

2. The event on the other class needs to be visible to you (ie: public or internal).

3. Subscribe on a valid instance of the class, not the class itself.